1. Technical Field
The present invention relates to a semiconductor device and a method of fabricating a semiconductor device.
2. Related Art
In accompaniment with the spread of system-in-package technologies in recent years, processing techniques for thinning semiconductor wafers have been receiving attention. For example, in the field of stack packages used in mobile telephones and so forth, products in which plural chips that have been thinned to 100 μm or less are stacked inside a package are being developed. Processing for thinning a semiconductor wafer is performed by forming circuit elements and so forth on the semiconductor wafer and thereafter using a back-grinding wheel to grind the back surface of the wafer. As the thinning of the semiconductor wafer progresses, chipping, chip breakage, and warping of the semiconductor wafer occur, and the problem of a drop in yield and a drop in productivity occurs. In order to solve this problem, the technique of leaving about 3 mm, for example, of the outer peripheral portion from the outer edge of the semiconductor wafer and grinding and thinning only the inner peripheral portion of the semiconductor wafer is known. Introducing this technique makes it possible to reduce wafer conveyance risks and warping.
Japanese Patent No. 4,749,849 describes a wafer that has an annular reinforcement on the outer periphery of the back surface of the wafer, with the entire back surface of the wafer being covered with a metal film, wherein the positions of streets formed on the front surface of the wafer are detected by removing the metal film on the annular reinforcement, and the wafer is cut from the back surface side along the streets that have been detected.
Further, Japanese Patent Application Laid-Open (JP-A) No. 2008-187148 describes forming a rib structure on the back surface of a semiconductor wafer by removing the back surface of the semiconductor wafer to a predetermined depth while leaving a predetermined width from the outer peripheral end portion, forming a metal electrode film on the back surface of the semiconductor wafer on which the rib structure has been formed, forming a semiconductor wafer cutting position adjustment mark on the back surface of the semiconductor wafer on the basis of the position in which a front surface-side element structure portion captured by a camera disposed on the front surface side of the semiconductor wafer is formed, and cutting the semiconductor wafer into chips by using this cutting position adjustment mark.
In the dicing step of separating the semiconductor wafer into chips, ordinarily dicing tape is adhered to the back surface side of the semiconductor wafer and the semiconductor wafer is set in a dicing machine with the semiconductor wafer being supported on the dicing tape. Thereafter, dicing is performed by running a dicing blade along dicing lines or scribe lines defined on the front surface of the semiconductor wafer.
However, a semiconductor wafer that has been thinned by grinding only the inner peripheral section of the back surface of the semiconductor wafer such as described above has a step-like difference in height between its outer peripheral portion and its inner peripheral portion. Adhering dicing tape to the back surface of a semiconductor wafer having such a step-like difference in height to thereby stably support the semiconductor wafer is difficult. For this reason, the outer peripheral section of the back surface of the semiconductor wafer is ground, so that the back surface of the wafer is flattened, in another grinding step after a back surface electrode formation step and an inspection step. However, in this case, two grinding steps become necessary, which leads to an increase in costs. For this reason, adhering the dicing tape to the front surface side of a wafer not having a step-like difference in height and performing dicing from the back surface side of the wafer is preferred. In the case of performing dicing from the back surface side of the wafer, it is necessary to run the dicing blade along dicing lines defined on the front surface side of the wafer.
Here, if the device is one that outputs electric current from the back surface of the semiconductor chip, a metal film configuring a back surface electrode is formed on the back surface of the wafer before the semiconductor wafer is separated into chips. This metal film has the role of imparting solder wettability and conductivity to the back surface side of the semiconductor chip. Consequently, in the dicing step, the metal film configuring the back surface electrode is also cut at the same time together with the semiconductor wafer. However, there is the problem that when the dicing blade cuts the metal film together with the semiconductor wafer, the dicing blade tends to become stuck and the life of the dicing blade becomes shorter.